Van Diemen's Land
In 1832, Montagu acted as colonial treasurer, and in 1834, was appointed colonial secretary. Montagu was still in this position when Sir John Franklin became governor in 1836, and for five years the two worked in harmony. Montagu devoted time to the question of convict discipline, and in 1841, prepared the necessary instructions for a probation system which was then established.
In October 1841, a strong difference of opinion arose with governor Franklin over the reinstatement by Franklin of a surgeon who had been dismissed after being charged with culpable negligence. Franklin reinstated him because he thought that further evidence showed the penalty to have been unjust, Montagu declared that the reinstatement would degrade the colonial secretary's office, and that if Franklin persisted in his determination he must not expect the same assistance from the colonial secretary that had been hitherto given. Franklin would not be intimidated and friction continued for some time.
On 17 January 1842, in writing to Franklin, Montagu said, "while your excellency and all the members of your government have had such frequent opportunities of testing my memory as to have acquired for it the reputation of a remarkably accurate one, your officers have not been without opportunity of learning that your excellency could not always place implicit reliance upon your own."[2] In the circumstances this could only be taken as insulting, and Franklin feeling there was no possibility of their working together, dismissed Montagu from his office. Montagu withdrew the offending phrase but Franklin's mind was made up. Montagu, however, went to England and so successfully brought his case before Lord Stanley, the Secretary of State for War and the Colonies, that Governor Franklin was recalled.
Cape Colony
In April 1843, Montagu took up duties as colonial secretary to the Cape Colony, where he did useful work. Soon after his arrival he "ascertained that there was a large amount of revenue many years overdue, and set about collecting it with an intensity of purpose from which even pity for the distressed was absent".[3]
Montagu introduced a system of constructing roads by convict labour, and worked with great energy for the good of the colonies in many other directions. Montagu Pass near George, built by an Australian named Henry Fancourt White in 1843–1847, was named in his honour, as was the town of Montagu. Over-work on constitutional changes which were taking place in the government, led to a nervous breakdown in 1852, and on 2 May, he left for England.
He never fully recovered his health and died on 4 November 1853. He is buried at Brompton Cemetery, London.